1. Field of the Invention
This invention relates to electronic engine control of an internal combustion engine.
2. Prior Art
The primary function of an Enhanced Distributorless Ignition System (EDIS) is to deliver a full energy spark at a crank angle calculated by an Electronic Engine Controller (EEC). The EDIS module determines the engine position using a high data rate crankshaft position sensor such as a variable reluctance sensor (VRS). The EDIS module generates a profile ignition pickup (PIP) signal from the high data rate VRS crankshaft position signal. The EEC uses this PIP signal to determine fuel scheduling, engine RPM and engine position.
The EDIS module synchronizes to the signal produced by the VRS sensor. The signal produced by the VRS sensor is proportional to a crankshaft mounted 36 tooth wheel. One of the teeth in this wheel is selectively removed to coincide with cylinder number one pair and is termed a missing tooth. Cylinder number one pair indicates the position of the crankshaft at either cylinder number one and its opposite cylinder having a common ignition coil.
Using a base algorithm during initial synchronization, the EDIS module requires three VRS teeth, following the missing tooth in order to synchronize to engine position. A plot of the signals representing VRS, PIP, fuel injector firing and ignition coil firing signal during synchronization is shown in FIGS. 1A, 1B, 1C, and 1D, respectively. The time required for synchronization depends on engine stall position. With noise coupled to the VRS signal it becomes harder to differentiate true engine rotation from noise. A software VRS filter algorithm is used to determine the true VRS signal.
In the base algorithm the EDIS module synchronizes to the missing tooth and puts out the PIP signal to the EEC. The EEC will then inject fuel into the cylinder after a valid PIP signal edge is received. The fuel must go through an intake and compression stroke before the air/fuel mixture is ready to ignite. This causes the first spark to be wasted since there was no air/fuel mixture to be ignited in the cylinder receiving the spark. The result of using such a base algorithm is longer and inconsistent start times.
Also known is U.S. Pat. No. 4,131,098 which teaches a hardware ignition system to generate a spark event at the earliest top dead center engine position. This patent does not teach delaying the spark event until an air/fuel mixture is available to be ignited in a cylinder. Further, this patent does not teach a system adaptable to a distributorless ignition system.
U.S. Pat. No. 4,656,993 teaches a system for identifying the position of specific engine cylinders. The patent does not teach improving start times.
U.S. Pat. No. 4,515,131 teaches reducing engine start times by providing engine combustion at the earliest possible event, within one crankshaft revolution by using both a crankshaft angle sensor and a cylinder discrimination signal. It would be desirable to need only a crankshaft angle sensor and not have a need for a cylinder discrimination signal. There is taught a method and apparatus for igniting an air/fuel mixture within one rotation of the engine crankshaft by injecting fuel on the first crankshaft angle signal after the start of cranking. In FIG. 3 of patent '131 at indication (2) is a crank angle signal N, and at indication (3) is a cylinder discrimination signal G, indicating true engine position. At indications (4)-(9) are timing charts for cylinders 1-6 showing intake in ignition for each cylinder. Indications (10)-(12) show the system when engine cranking, as determined from a starter signal, occurs at various times in the engine cycle with reference to indications (4)-(9) above. As to indications (10)-(12), all have in common injecting fuel FU in accordance with the first crank angle signal after the start of cranking CR, thereby achieving a faster engine starting time. This can be contrasted with another prior art system shown in FIG. 4 of patent '131 in which fuel injection FU occurs after cylinder discrimination signal G (2) with cranking CR occurring between G (1) and G (2).
Thus, the system of patent '131 as shown in FIG. 3 requires the cylinder discrimination signal G as well as the crank angle signal to schedule fuel. It would be desirable to have an algorithm that would not require a cylinder identification signal to schedule fuel injection time. Indeed, it would be desirable to avoid the time delay caused by first locating true engine position before injecting fuel. These are some of the problems this invention overcomes.